1. Field
The present embodiments generally relate to ballast systems for a marine structure. The ballast system comprises a ballast tank and a pump. The pump comprises a low side and a high side and the ballast system comprises a first inlet conduit assembly adapted to provide a fluid communication between the ballast tank and the low side. The ballast system is adapted to provide a first operating condition in which first operating condition a fluid is pumped from the low side to the high side.
2. Description of the Related Art
A marine structure, such as a ship or a semi-submersible unit, is often provided with one or more ballast systems in order to control the draught and/or the inclination of the marine structure. Generally, a ballast system comprises a ballast tank, and in fact often a plurality of tanks, which is adapted to be filled with sea water—i.e. water ambient of the marine structure—through a water filling assembly.
In order to be able to empty the ballast tank, the ballast system further generally comprises a pump assembly which in turn comprises a pump and means for fluidly connecting the tank and the pump as well as means for connecting the pump and the environment ambient of the marine structure such that water may be pumped from the tank to the ambient environment. Generally, at least a portion of the pump assembly is in fluid communication with the aforesaid water filling assembly.
However, when a ballast tank is filled with water, there is a risk that air will be mixed with the water such that air will be entrained in the water filling assembly and—at a later stage—in at least a portion of the pump assembly. As such, when a ballast tank is to be emptied of water, there is a risk that the air in the pump assembly will be guided towards the pump and hence introduced in the pump. Since air generally adversely effects a pump, the presence of air is undesired.
Moreover, at the completion of a ballast tank emptying operation, i.e. when a ballast tank is almost completely emptied of water, the water flow from the ballast tank to the pump is generally lower than in the beginning of the ballast tank emptying operation. Since a pump generally has an optimum operating condition at a specific combination of the flow rate and pressure, the aforesaid change in the water flow is generally undesired.
Additionally, during load altering operations of the marine structure, such as multiple ballast operations and/or oil refuelling, which occur simultaneously as a ballast tank emptying operation, there may be a need for controlling the rate at which the ballast tank is emptied in order to maintain a balance in the marine structure. Moreover, when a ballast tank is almost emptied of water, it may be desirable to have a low flow rate of the water leaving the ballast tank in order to at least limit the amount of air in the water entering the pump.
In view, of the above, a need for improvements in the field of ballast systems exists.